In accordance with the progress of digital technology, recent years have seen an increasing tendency for high-speed processing or storage of a large volume of data. This is creating a demand for higher integration and higher performance of a semiconductor device used for electronic apparatuses.
Under such circumstances, in order to realize higher integration of a semiconductor memory device (DRAM), many researches and developments are underway on a technique to use a ferroelectric material or a high-dielectric constant material, in place of a silicon oxide or a silicon nitride, in forming a capacitor insulating film of a capacitor element constituting a DRAM.
Further, in order to realize a nonvolatile RAM capable of high-speed writing operation and reading operation with low voltage, also under active research and development is a ferroelectric memory (FeRAM) using, as a capacitor insulating film, a ferroelectric film having a spontaneous polarization characteristic.
A ferroelectric memory stores data by utilizing a hysteresis characteristic of a ferroelectric. In the ferroelectric memory, a ferroelectric capacitor having a ferroelectric film as a capacitor dielectric film formed between a pair of electrodes is provided in each memory cell. In a ferroelectric, polarization occurs according to voltage applied between the electrodes, and spontaneous polarization remains even if the applied voltage is removed. Further, polarity inversion of the applied voltage results in polarity inversion of the spontaneous polarization. Therefore, by detecting the spontaneous polarization, it is possible to read data. The ferroelectric memory has characteristics of high-speed operation, low power consumption, excellent read/write durability, and so on.
However, to design and manufacture a ferroelectric memory, it is necessary to overcome the property that an electric characteristic of its ferroelectric capacitors is easily deteriorated by hydrogen gas and moisture entering from an external part. In a conventional ferroelectric capacitor which includes a bottom electrode composed of a Pt film, a ferroelectric film composed of a PbZr1-xTixO3 (PZT) film, and a top electrode composed of a Pt film, if a substrate is heated to about 200° C. in an atmosphere of an about 40 Pa (0.3 Torr) hydrogen partial pressure, the ferroelectric characteristic of the PbZr1-xTixO3 film is almost completely lost. Moreover, if the thermal treatment is applied in a state where the ferroelectric capacitor adsorbs moisture or in a state where moisture exists near the ferroelectric capacitor, the ferroelectric characteristic of the ferroelectric film greatly deteriorates.
Under such circumstances, in manufacturing a ferroelectric memory, processing that generates as little moisture as possible and can be conducted at as low temperature as possible is selected after the ferroelectric film is formed. In particular, in forming an interlayer insulating film, a CVD (Chemical Vapor Deposition) method or the like using source gas generating a relatively small amount of hydrogen is selected.
Further, there have been proposed a structure including a barrier film covering a ferroelectric capacitor and a structure including a barrier film formed above a ferroelectric capacitor. As the barrier film, an aluminum oxide film is mainly used. This is because the aluminum oxide film has a function of preventing diffusion of hydrogen and moisture.
However, it is difficult to form contact holes in a desired shape passing through the aluminum oxide film. This is because the aluminum oxide film little reacts with etching gas and thus sputtering etching is required. Reducing the thickness of the aluminum oxide film enables an increase in processing accuracy, but cannot ensure a sufficient barrier effect due to relatively low coverage of the aluminum oxide film.
Patent document 1: Japanese Patent Application Laid-open No. 2002-176149
Patent document 2: Japanese Patent Application Laid-open No. 2004-71932
Patent document 3: Japanese Patent Application Laid-open No. 2001-111007